Traditionally, Skid-Steer® Loader Machines as made famous by manufacturers such as Bobcat® and the like have been powered almost exclusively by hydraulics. Skid-Steer® is a registered trademark of Arts-way Manufacturing Co., Inc., a Delaware Corporation. Bobcat® is a registered trademark of Clark Equipment Company of New Jersey.
These machines traditionally have gasoline or diesel internal combustion engines that drive a hydraulic pump. The pump usually provides power to two independently controlled hydraulic motors one for each side of the machine. The output of each motor drives a drive sprocket with two sets of sprocket teeth. One set of sprocket teeth drives a chain that goes to a front wheel sprocket and the other set of sprocket teeth drives a chain that goes to the rear wheel sprocket. The hydraulic pump also provides power for lifting functions and power takeoffs for implements that can be connected to the machine.
U.S. Pat. No. 4,705,449 to Christianson et al. discloses the use of two electric traction motors. FIG. 1 is a plan view of an electric drive system of U.S. Pat. No. 4,705,449 to Christianson et al. wherein battery 28 supplies electric power to two traction motors 60, 64 which in turn are coupled 84 to a gear reducer 82. Specifically, the '449 patent states at col. 4 line 10 et seq.: “a first traction motor 60 provides the motive force for the left-hand side of the vehicle and a second traction motor 64 provides the motive force for a right-hand side of the vehicle 66. Both the first traction motor 60 and the second traction motor 64 are powered by a battery pack 28 . . . . Similarly, the traction motor 64 is connected to a spur gear reduction assembly 82 through a coupling 84. The spur gear reduction assembly engages a chain 86 which in turn engages a right rearward gear 74 and left forward gear 90, which are respectively connected to wheels 14a and 14b through axles 92 and 94. As will be appreciated, the traction motor 60 is operated independently of the traction motor 64 thereby permitting the wheels 14c, 14d to operate at different speed than wheels 14a and 14b to create skid steering.”
U.S. Pat. No. 4,705,449 to Christianson et al. discloses the use of two electric traction motors. The motors are not identified by type in Christianson et al as either DC or AC. However, the motors are DC electric motors as they are controlled by a device identified in the '449 patent to Christianson, namely, a General Electric EV 1 SCR Controller, which is designed to control DC motors. The General Electric EV 1 SCR Controller describes the use of rectifiers to pulse power to DC motors and has no provision for the control of AC motors.
A copy of the EV 1 SCR Controller technical literature is submitted herewith in an Information Disclosure Statement and describes the use of the controller as being for the control of DC motors. Additionally, the EV 1 SCR Controller is identified in U.S. Pat. No. 4,265,337 to Dammeyer entitled Fork Lift Truck Speed Control Upon Fork Elevation and is used to control a DC motor 92.
Additionally, the EV 1 SCR Controller has been used in numerous automobiles (electric vehicles) in conjunction with DC series wound motors which provide high current and high torque at low rpm.
DC traction motors have been used in applications involving forklifts and similar vehicles in the past. Internal combustion engines are not favored in such applications because an internal combustion engine produces zero torque at zero engine speed (RPM) and reaches its torque peak later in its operating range. Internal combustion engines generally require a variable-ratio transmission between the engine and the wheels to match engine speed to the road speeds and loads encountered. A clutch must be provided so that the engine can be mechanically decoupled from the wheels when the vehicle stops. Additionally, some slippage of the engine with respect to the drive train occurs while starting from a stop. Direct current electric traction motors produce considerable torque at zero RPM and thus may be connected directly to the wheels. Alternating current motors, hydraulic motors and pneumatic motors also produce torque at zero RPM.
Although the term traction motor is usually referred to in the context of a direct current motor, the term is also applicable to alternating current motor applications as well. Additionally, the term traction motor is used to describe any motor of whatever type used to supply torque and power to a vehicle's wheel, tracks, etc.
In small utility vehicles and the like, space is an important consideration in the design of the vehicle. It is therefore desirable to use a small motor, electric, hydraulic, or pneumatic which is capable of supplying required torque and horsepower under all operating conditions. If an electric motor is used it may be an alternating current motor or it may be a direct current motor.
Generally, for a given power, high speed electric motors are smaller in size, lighter in weight, and less expensive than low speed motors. Generally, for a given power, alternating current motors are smaller than direct current motors.
Therefore, it is highly desirable to save space, weight and cost in the powertrain of a utility vehicle through the use of a high speed motor so that the space may be used for batteries, controls or other components.